1. Field
This invention relates to pharmaceutical compositions generally, and to stabilized aqueous solutions of certain antidepressant drugs specifically.
2. State of the Art
Solutions of certain antidepressants (e.g., amitriptyline) are not very stable. They discolor, form particles, and/or suffer a decrease in concentration under certain conditions. For example, they may discolor or show a decrease in concentration upon exposure to light; upon the formation of peroxides in, or addition of peroxides to, the solutions; or when such solutions are stored at elevated temperatures. Particles may also form in such solutions under these conditions. Discoloration, development of opalescence, a decrease in concentration, and particle formation are all tokens of instability. These tokens of instability may occur rather rapidly, sometimes within days, forcing the dispensing pharmacist to mix new solutions frequently.
An attempt to stabilize dry pharmaceutical preparations containing amitriptyline oxide dihydrate is described in German Patent Application DE 3247676 A1, published on Jun. 28, 1984 (corresponding to U.S. Pat. No. 4,567,202). That patent application describes a composition containing amitriptyline oxide dihydrate and an organic acid including certain listed amino acids. The organic acid, especially citric acid, is used to stabilize the amitriptyline.
GB 2,082,910A to Berk Pharmaceuticals Ltd. (published on Mar. 17, 1982) describes a pharmaceutical composition (e.g. a syrup) comprising amitriptyline and L-tryptophan in an inert carrier. The L-tryptophan reportedly acts to reduce side-effects associated with the amitriptyline.
EP 93,373A (corresponding to U.S. Pat. No. 4,603,131) to Abbott Laboratories describes a liquid pharmaceutical composition useful for preventing irritation of the nasal mucousal membrane. The composition contains a tri-cyclic antidepressant, certain buffers, and "preservatives". The preservatives listed include: benzalkonium chloride, edetate disodium, sodium bisulfate, phenylmercuric acetate, cetylpyridinium chloride, thimerosal, chlorobutamol, cetyltrimethyl ammonium bromide, methylparaben, propylparaben, and butylparaben.